Tremolo or vibrato producing apparatus including rotating or oscillating raffle

ABSTRACT

The sound channel of a rotating baffle for creating a tremolo effect is, as seen by the sound transducer that &#39;&#39;&#39;&#39;fires&#39;&#39;&#39;&#39; into the channel, substantially a semiparabola of revolution.

United States Patent Inventor Appl. No.

Filed Patented Assignee Lawrence A. Muma Kitchener, Ontario, Canada 859,016

Sept. 18, l 969 Apr. 20, l 97 1 Electrohome Limited Kitchener, Ontario, Canada TREMOLO OR VIBRATO PRODUCING APPARATUS INCLUDING ROTATING OR OSCILLATING RAFFLE 6 Claims, 5 Drawing Figs.

US. Cl 181/27, 1 81/3 1 Int. Cl ..Gl0k1l/l0, 1-104r 1/34 Primary ExaminerStephen J. Tomsky Attorney-Peter W. McBurney ABSTRACT: The sound channel of a rotating baffle for creating a tremolo effect is, as seen by the sound transducer that fires into the channel, substantially a semiparabola of revolution.

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SHEET 1 OF 2 TONE SIGNAL GENERATOR I N VEN TOR.

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TREMOLO OR VIBRATO PRODUCING APPARATUS INCLUDING ROTATING OR OSCILLATING RAFFLE This invention relates to apparatus for acoustically adding vibrato or tremolo to sound, e.g., musical sounds produced by an electronic organ.

Systems for creating a tremolo or vibrato effect employing rotating baffles are well known, see, for example, US. Pat. No. 2,869,667, D. J. Leslie, Jan. 20, 1959 and US. Pat. No. 3,3l5,760, J. M. Schwendener, Apr. 25, I967. The rotating baffle shown in the latter patent has a sound channel defined by two straight spaced-apart parallel sides and a generally arcuate base, and, like the rotating baffle shown in US. Pat. No. 3,174,579, D. J. Leslie, by the very nature of its construction results in multiple reflections of high-frequency (short wavelength) sounds. Baffles of this type have relatively poor high-frequency responses and alter the character of sounds simulating those of string instruments such as violins.

Moreover, baffles of this type are relatively expensive to make.

Rotating baffles of the inclined, flat plate type shown in US. Pat. No. 2,869,667 have good high-frequency response but relatively poor low-frequency response due to the leakage of air past the bafiles. In addition, the directional or beaming effect of such flat plate baffles is relatively poor.

In accordance with the instant invention there is provided a bafile for a tremolo or vibrato system that has good highfrequency and low-frequency response, is relatively simple and inexpensive to make and is quite efficient. These advantages are achieved with a bafile having a sound channel that, as seen by the sound transducer that fires into it, is substantially a semiparabola of revolution.

This invention will become more apparent from the following detailed description, taken in conjunction with the appended drawings, in which:

FIG. I is a top elevation showing two baffles embodying this invention after moulding and prior to separation;

FIG. 2 is a section taken along line 2-2 in FIG. 1;

FIG. 3 is a side elevation of one of the two battles shown in FIG. I after separation;

FIG. 4 is a side view, partly in section, of apparatus embodying this invention for adding tremolo or vibrato to sound; and

FIG. 5 is a side elevation, partly in section and somewhat schematic, of another embodiment of this invention.

Referring to FIG. 3, there is shown a baffle embodying this invention. Two such baffles 10 and 11 joined together along a line 12 that subsequently is cut are shown in FIG. I. The article shown in FIG. I and also in section in FIG. 2 is moulded of a suitable material such as expanded polystyrene. As best seen in FIG. 1, it is circular in cross section in the plane of the paper, but, as best shown in FIGS. 2 and 3, in the opposite plane has an interior surface 13 that is generally parabolic in configuration.

Moulded integral with the article are two seats 14 to which the am of a counterweight may be secured, as will be explained in greater detail hereinafter. Also moulded integral with the article are reinforcing steps I5 each containing an aperture 16 therein. Aperture l6 defines the rotational axes of the two baffles wand 11.

It will be seen by reference to FIG. I that the axis of rotation of each baffle is displaced inwardly of the center of curvature of the circular part of interior surface 13 of each baffle, this center of curvature being designated 17. Thus, as seen from any point on a line passing through the center of curvature 17 and perpendicular to the plane of FIG. I, the interior surface 13 of each battle is semicircular. On the other hand, as seen from any point on the axis of rotation of each baffle, surface 13 is substantially parabolic. In other words, with reference to axis of rotation 16, interior surface 13 is substantially a semiparabola'of revolution.

It is difiicult to mould a semiparabola of revolution, but by making surface 13 parabolic as shown in FIG. 2 and eccentric with respect to center of curvature 17, a semiparabaloid of revolution results with respect to rotational axis 16. Such a configuration is an important feature of this invention, as it has been found that if interior surface 13 is shaped in the fonn of a quarter of a sphere, it will have poor acoustic qualities compared to a baffle embodying this invention.

As noted above, two baffles embodying-the invention are moulded as a single unit as shown in FIGS. I and 2, which makes for economical manufacture, and then are separated along line 12 to provide two baffles of the type shown in FIG. 3.

Turning now to FIG. 4, baffle 10 is shown in cross section and is positioned between a baffle board 18 containing a circular opening I9 therein and a board 20 on which is mounted a bearing 21. Rotatably mounted in bearing 21 is a shaft 22 that passes through opening l6-and which, at one end thereof, has keyed or otherwise secured thereto the arm 23 of a counterweight 24. Counterweight 24 is secured to arm 23 by means of a bolt 25 that passes through an elongated slot (not shown) in am 23 and threadably engages counterweight 24. By this means the position of the counterweight and the balancing efi'ect thereof may be varied. The other end of arm 23 is fastened to seat 14 by means of a'screw 26.

Secured to the opposite end of shaft 22 is a pulley 27 over which is trained a belt 28 that passes over another pulley 29 secured to the shaft 30 of an electric motor 31, preferably of the variable speed type. Of course other systems for rotating baffle 10 could be employed without departing from this invention.

Mounted on baffle board 18 over opening 19 is a sound transducer in the form of a loudspeaker 32. Loudspeaker 32 is connected to any suitable tone signal generator 33, e.g., the tone signal generator of an electronic organ.

In operation, when a tremolo or vibrato effect is desired, motor 31 is turned on by the player causing rotation of baffle 10. The speed of rotation of the baffle and hence the frequency of the tremolo may be varied by changing the speed of motor 31.

As shown in FIG. 4, the longitudinal axis of loudspeaker 32 coincides with the axis of rotation of baffle 10, so that the shape of interior surface 13 as seen by loudspeaker 32 is substantially that of a semiparabola of revolution. Loudspeaker 32 fires into the sound channel defined by interior surface 13 producing a tremolo or vibrato effect as the baffle rotates. As a result of the shaping of bafile, there is only a single sound reflection, so the high frequency response of the baffle is excellent. The low frequency response of the baffle also is excellent, and a pronounced directional effect is achieved because of the particular shaping, the sound being beamed by the sound channel.

The embodiment of the invention shown in FIG. 5 differs from that shown in FIG. 4 in that three loudspeakers 32a, 32b and -32c are employed, the speakers being high-frequency, midrange and low-frequency loudspeakers. Each loudspeaker has its own cylindrical enclosure 34a, 34b and 340 embodiment of FIG. 4.

. at different speeds, and not only is a tremolo or vibrato effect semicircular as shown in FIG. I and the axis of rotation/ With such an arrangement sound is radiated in a hemispherical pattern from the backs of the diaphragms of the loudspeakers, and baffles 10 are so mounted as to partly enclose each loudspeaker. It will be understood that these loudspeakers fire into the baffles.

In the embodiment of FIG. 5, pulleys 27 that differ in size from each other are employed with belt 28 being trained over the three pulleys and over pulley 29.

With the system shown in FIG. 5, the three baffles 10 rotate created, but also a chorus effect is produced, this being attributable to the different rotational speeds of the baffles.

It should be noted that one important result of having loudspeaker 32 mounted on axis of rotation of baffle 10 is an enhanced Doppler effect, because any part of baffle always is moving relative to a given sound wave and consequently is always either pulling or pushing that sound wave.

Those skilled in the art will appreciate that while the preferred embodiment of this invention has been disclosed herein, changes and modifications may be made thereinwithout departing from the spirit and scope of this invention as defined in the appended claims.

I claim:

1. In apparatus for acoustically adding vibrato or tremolo to sound of a type comprising: a baffle having an axis of rotation; means for rotating said baffle about said axis of rotation; a sound transducer juxtapositioned with respect to said baffle to direct sound produced by said sound transducer into said baffle to reflect off the interior surface of said bafile; the improvement wherein the shape of said interior surface of said bafile as seen by said sound transducer is substantially a semiparabola of revolution, said interior surface being semicircular in cross section in a first plane perpendicular to said axis of rotation and substantially parabolic in cross section in a second plane that is perpendicular to said first plane and that includes said axis of rotation, said axis of rotation being displaced inwardly of the center of curvature of said semicircular cross section, said sound transducer having a 4 longitudinal axis, said longitudinal axis coinciding with said axis of rotation. Y

2. The invention according to claim 1 wherein said sound transducer is a loudspeaker.

3. The invention according to claim 2 including an enclosure, said loudspeaker being mounted in inverted cone relationship on said enclosure and between said enclosure and said baffle.

4. The invention according to claim 1 wherein there are a plurality of said loudspeakers and a corresponding number of said baffles, and wherein said means for rotating said baffles comprise means for rotating said bafiles at different speeds from one another.

5. Apparatus for acoustically adding vibrato or tremolo to sound comprising a plurality of baffles each having an axis of rotation; means for rotating said baffles about saidaxes of rotation at different speeds from one another; a plurality of sound transducers juxtapositioned with respect to said baffles to direct sound produced by said sound transducers into said baffles to reflect off the interior surfaces of said baffles; the shape of the interior surfaces of said baffles as seen by said sound transducers being substantially semiparabolas of revolution.

6. The invention according to claim' 5 wherein said sound transducers are loudspeakers. 

1. In apparatus for acoustically adding vibrato or tremolo to sound of a type comprising: a baffle having an axis of rotation; means for rotating said baffle about said axis of rotation; a sound transducer juxtapositioned with respect to said baffle to direct sound produced by said sound transducer into said baffle to reflect off the interior surface of said baffle; the improvement wherein the shape of said interior surface of said baffle as seen by said sound transducer is substantially a semiparabola of revolution, said interior surface being semicircular in cross section in a first plane perpendicular to said axis of rotation and substantially parabolic in cross section in a second plane that is perpendicular to said first plane and that includes said axis of rotation, said axis of rotation being displaced inwardly of the center of curvature of said semicircular cross section, said sound transducer having a longitudinal axis, said longitudinal axis coinciding with said axis of rotation.
 2. The invention according to claim 1 wherein said sound transducer is a loudspeaker.
 3. The invention according to claim 2 including an enclosure, said loudspeaker being mounted in inverted cone relationship on said enclosure and between said enclosure and said baffle.
 4. The invention according to claim 1 wherein there are a plurality of said loudspeakers and a corresponding number of said baffles, and wherein said means for rotating said baffles comprise means for rotating said baffles at different speeds from one another.
 5. Apparatus for acoustically adding vibrato or tremolo to sound comprising a plurality of baffles each having an axis of rotation; means for rotating said baffles about said axes of rotation at different speeds from one another; a plurality of sound transducers juxtapositioned with respect to said baffles to direct sound produced by said sound transducers into said baffles to reflect off the interior surfaces of said baffles; the shape of the interior surfaces of said baffles as seen by said sound transducers being substantially semiparabolas of revolution.
 6. The invention according to claim 5 wherein said sound transducers are loudspeakers. 